There are numerous information's already given in the question. Based on those information's the answer can be easily deduced.
Ratio of men to women = 3 : 5
Total number of men = 51
Now
Men/Women = 3/5
51/women = 3/5
3 Women =51 * 5
3 Women = 255
Women = 255/3
= 85
Then
Total number of employees = 51 + 85
= 136
From the above deduction, it can be concluded that the total number of employees in the company is 136. I hope the procedure is clear enough for you to understand.